This invention relates to a method and an apparatus for recognizing particle impurities, such as trash fragments, neps, shell neps, burls and the like in textile fibers such as cotton, chemical fibers and the like. The determination of the degree of impurities (trash content) of the fiber is effected by electron-optical means: the fiber is scanned by a sensor and the measuring values are applied to an image processing device.
Neps are fiber knots smaller than approximately 1 mm, while shell neps are grain shell fragments which have grown-on fibers. Burls, on the other hand, are fiber knots that are greater than approximately 1 mm and trash particles are, for example, leaf and shell fragments. Elongated trash particles (bark, grass or stem fragments) form a special class (subclass), whose length/width ratio is large. These particle impurities are summarized in FIG. 10.
In a known process for cleaning and opening fiber to obtain fiber tufts, the fiber material passes through a feeding device and is thereafter submitted to a cleaning process. The degree of fiber impurity is determined during the supply of the fiber material to the cleaner.
For performing the known impurity detecting process, between a feeding device and an opening/cleaning device a measuring line (measuring section) is provided for the fiber material. The measuring line comprises a channel-like guide having a transparent plate which is illuminated by a lamp and a conveyor belt which serves for pressing the fiber layer in the channel against the transparent plate, whose distance from the conveyor belt is approximately 2-4 cm. The measuring line further comprises a camera which applies signals to a grey scale value comparator, a counter and a computer. This apparatus serves for improving the cleaning process performed by the cleaner which receives the fiber material. The fiber material which is discharged by the cleaning device is introduced to a carding machine or a roller card unit.
It is a disadvantage of the above-outlined process that the fiber tuft layer supplied to the cleaner is approximately 2-4 cm thick so that only impurities on the surface may be detected whereas those inside the material remain undetected. It is a further disadvantage of known processes that of the impurities determined on the surface in a reflecting light only a percent proportion in relation to the fibers can be summated. It is also a drawback that impurities such as neps, shell neps and burls which have a particularly adverse effect on the usual spinning processes cannot be detected.